Answer: 80%
15 are on the council, so 75-15 = 60 are not on the council. Therefore, 60/75 = 0.80 = 80% of the students aren't on the council.
An alternative way to find this answer is to compute 15/75 = 0.20 = 20% showing that 20% of the students are on the council, so 100% - 20% = 80% are not on the council.
